package org.apache.lucene.index;


/**
 * A Term represents a word from text.  This is the unit of search.  It is
 * composed of two elements, the text of the word, as a string, and the name of
 * the field that the text occured in, an interned string.
 * <p>
 * Note that terms may represent more than words from text fields, but also
 * things like dates, email addresses, urls, etc.
 * 表示文本中的一个单词
 * 搜索的基本单元
 */
public final class Term implements Comparable, java.io.Serializable {
  String field;
  String text;

  /**
   * Constructs a Term with the given field and text.
   */
  public Term(String fld, String txt) {
    this(fld, txt, true);
  }

  Term(String fld, String txt, boolean intern) {
    field = intern ? fld.intern() : fld;    // field names are interned
    text = txt;            // unless already known to be
  }

  /**
   * Returns the field of this term, an interned string.   The field indicates
   * the part of a document which this term came from.
   */
  public final String field() {
    return field;
  }

  /**
   * Returns the text of this term.  In the case of words, this is simply the
   * text of the word.  In the case of dates and other types, this is an
   * encoding of the object as a string.
   */
  public final String text() {
    return text;
  }

  /**
   * Compares two terms, returning true iff they have the same
   * field and text.
   */
  public final boolean equals(Object o) {
    if (o == null)
      return false;
    Term other = (Term) o;
    return field == other.field && text.equals(other.text);
  }

  /**
   * Combines the hashCode() of the field and the text.
   */
  public final int hashCode() {
    return field.hashCode() + text.hashCode();
  }

  public int compareTo(Object other) {
    return compareTo((Term) other);
  }

  /**
   * Compares two terms, returning an integer which is less than zero iff this
   * term belongs after the argument, equal zero iff this term is equal to the
   * argument, and greater than zero iff this term belongs after the argument.
   * <p>
   * The ordering of terms is first by field, then by text.
   */
  public final int compareTo(Term other) {
    if (field == other.field)        // fields are interned
      return text.compareTo(other.text);
    else
      return field.compareTo(other.field);
  }

  /**
   * Resets the field and text of a Term.
   */
  final void set(String fld, String txt) {
    field = fld;
    text = txt;
  }

  public final String toString() {
    return field + ":" + text;
  }

  // 从流中读取数据，填充当前类
  private void readObject(java.io.ObjectInputStream in) throws java.io.IOException, ClassNotFoundException {
    in.defaultReadObject();
    field = field.intern();
  }
}
